Invite a friend to take down any book he pleases from the bookshelves, open it haphazard and choose a word in the first nine lines of any page but not later than the ninth word in the line.
Ask him to multiply the number of the page by 10;
add 25;
and then add the number of the line.
The result thus obtained is to be multiplied by 10, and the number at which the word stands is to be added to the product.
Your friend is then to hand you the book closed, with a slip of paper on which he has written the figure last obtained.
After thinking for a few moments you can open the book and read out the word that he has chosen.
How ?
To obtain this surprising result, all that you have to do is to substract in your mind 250 from the amount given you on the slip of paper handed to you.
The last figure of the answer will give you the number at which the word stands in the line, the last but one the number of the line, and the remaining figures the number of page.
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